1. Field of the Invention
The invention concerns a screen-printable or dispensable active brazing paste for brazing a first aluminum oxide ceramic body to a second aluminum oxide ceramic body, and a dispensable active brazing paste for brazing an aluminum oxide ceramic body to a metal body, and processes for producing them.
The invention further concerns a process for producing an actively brazed bond between a first aluminum oxide ceramic body and a second aluminum oxide ceramic body using a first region of active brazing paste applied to the first aluminum oxide ceramic body by screen printing and a second region of active brazing paste covering the same area as the first region, applied to the second aluminum oxide body by screen printing, and a process for actively brazing a metal body inserted into a hole in an aluminum oxide ceramic body using a pad of active brazing paste applied by dispensing.
2. Description of the Related Art
U.S. Pat. No. 5,095,759 describes an active brazing paste for brazing a platinum electrode to an aluminum oxide ceramic body, in which the active brazing paste comprises:
as the active brazing alloy a 99.5%/0.5% mixture of a 98% Au/2% Ni powder and PA1 a titanium hydride powder, and PA1 as the organic vehicle, a gel of 1.25% hydroxypropylcellulose and 98.7% 1,2-propanediol, PA1 such that 90% of the active brazing paste is made up of the 99.5%/0.5% mixture and 10% is made up of the gel. PA1 as the active brazing material a hydrogenated powder of a Zr/Ni/Ti alloy or a Zr/Fe/Ti/Be alloy and, PA1 as an organic vehicle PA1 as the active brazing material a hydrogenated powder of a Zr/Ni/Ti alloy or a Zr/Fe/Ti/Be alloy and PA1 as an organic vehicle a mixture of PA1 as the active brazing material a hydrogenated powder of a Zr/Ni/Ti alloy or a Zr/Fe/Ti/Be alloy and, PA1 as an organic vehicle PA1 in a first step, in air or in a protective gas atmosphere, a specified amount of the powder is mixed with just enough vehicle that all the particles of the powder are wetted, and, PA1 in a second step, in air, the particles of the powder are completely dispersed mechanically in the vehicle. PA1 as the active brazing material a hydrogenated powder of a Zr/Ni/Ti alloy or a Zr/Fe/Ti/Be alloy and PA1 as an organic vehicle a mixture of PA1 in a first step, a specified quantity of powder is mixed, in air or in a protective gas atmosphere, with just enough vehicle that all the particles of the powder are wetted by the vehicle, and PA1 in a second step, in air, the particles of the powder are completely dispersed mechanically in the vehicle. PA1 as the active brazing material a hydrogenated powder of a Zr/Ni/Ti alloy or a Zr/Fe/Ti/Be alloy and, PA1 as an organic vehicle PA1 the first region is applied to the first aluminum oxide ceramic body and the second region is applied to the second aluminum oxide ceramic body PA1 then both regions are dried in air at about 100.degree. C. PA1 then the two regions with the two aluminum oxide ceramic bodies PA1 as the active brazing material a hydrogenated powder of a Zr/Ni/Ti alloy or a Zr/Fe/Ti/Be alloy and PA1 as an organic vehicle a mixture of PA1 the active brazing paste applied is heated in a reactor with temperatures increasing by a rate of about 1.5K/min up to about 400.degree. C. and heated at that temperature until the solvent has evaporated and the polymer has completely decomposed, and PA1 then the aluminum oxide ceramic body and the metal body are brazed under high vacuum in the same reactor at about 900.degree. C. PA1 The screen-printable active brazing pastes have the rheologic properties required for screen printing; that is, they have the necessary intrinsic viscosity and the necessary ability to wet the ceramic body and/or the metal body. PA1 The screen-printable and dispensable active brazing pastes are sufficiently stable to sedimentation. That is, the particles in the finished active brazing paste settle extremely slowly if at all. PA1 There is no chemical reaction in the active brazing pastes between the vehicle and the surface of the particles at ambient temperature, i.e. about 20.degree. C. PA1 When the vehicle decomposes thermally, no carbon-containing residues which could deactivate the active brazing compound during brazing remain on the surfaces of the powder particles. PA1 The active brazing pastes accordingly adhere very well to the ceramic and metal bodys, and even after brazing the adhesion, mechanical strength, and density of the brazed bonds are so outstanding that they do not tear off in the bending test. The breakage occurs only within the ceramic, and the soldered bonds remain vacuum-tight for a long time. PA1 The solvents evaporate in vacuum without residue, even below 200.degree. C. PA1 The vehicle of the screen-printable or dispensable active brazing pastes can be removed before brazing without leaving a residue and without causing difficulty, especially in a high vacuum (on the order of 10.sup.-9 bar=10.sup.-4 Pa) at no more than 400.degree. C., so that there are no residues on the bodies which are yet to be brazed. PA1 The spreading behavior of the active brazing pastes, that is, their ability to flow at the brazing temperature, is outstanding.
Thus, this state of the art shows that active brazing pastes are usually a dispersion of a powder of the metallic component of the active brazing paste in an organic vehicle. That, in turn, is a polymer in a solvent. The particles of the powder are as homogeneously distributed as possible in the vehicle, and thus intimately combined with it.
Various Zr/Ni/Ti alloys suitable for use as an active brazing material to braze a first aluminum oxide ceramic body to a second aluminum oxide ceramic body are described in U.S. Pat. No. 5,334,344. Foils are produced from the alloy by melt-spinning, and the shapes needed for brazing can be punched from the foils.
Various Zr/Fe/Ti/Be alloys are described in CA-A 22 11 471. They are also suitable as active brazing materials for brazing two aluminum oxide bodies together.
U.S. Pat. No. 5,431,744 describes how hydrogenated powders which do not lose hydrogen, but remain stable, in air can be produced.
A screen-printable active brazing paste and a dispensable active brazing paste are of interest in this invention with regard to their consistency.